This invention relates to a control device for controlling a central processing unit on instantaneous voltage drop.
A central processing unit may suffer from a voltage drop which occurs in a power source voltage during its operation. In a normal state, the central processing unit is not controlled by the control device and maintains its operation when the power source voltage has a normal level. On the other hand, the central processing unit may be controlled by a control device only during the instantaneous voltage drop. More particularly, when the power source voltage is reduced or dropped to a first level which is lower than the normal level, the central processing unit is controlled by the control device to be turned to a waiting state. When the power source voltage is further reduced to a second level which is lower than the first level, the central processing unit is controlled by the control device to be turned to a reset state or an initial state.
A conventional control device of the type described comprises an input voltage applying section which is connected to a power source providing a power source voltage and which is connected to the central processing unit through a back-up condenser. The input voltage applying section supplies the central processing unit with an input voltage which results from the power source voltage. The conventional control device further comprises first and second detecting sections which will be later described.
The central processing unit has an interrupt terminal and a reset terminal which are given a waiting signal and a reset signal from the first and the second detecting sections, respectively. The central processing unit is turned to the waiting state on receiving the waiting signal through the interrupt terminal while the central processing unit is turned to the reset state on receiving the reset signal through the reset terminal.
The first detecting section detects whether or not a level of the input voltage is lower than the first level. When the level of the input voltage is lower than the first level, the first detecting section supplies the interrupt signal to the interrupt terminal of the central processing unit to render the central processing unit into the waiting state. The second detecting section detects whether or not a level of the input voltage is lower than the second level. When the level of the input voltage is lower than the second level, the second detecting section supplies the reset signal to the reset terminal of the central processing unit to render the central processing unit into the reset state.
However, the conventional control device controls the central processing unit so that the central processing unit is put into the waiting state even when a slight voltage drop occurs in the power source voltage. As a result, the central processing unit is very often turned to the waiting state.
In addition, it is necessary with the above-mentioned structure to require a back-up condenser of large capacity so as to compensate the instantaneous voltage drop of the input voltage.